Conventional throttle bodies are mounted within the intake air stream of an internal combustion engine. Typically, a butterfly valve is employed to control the amount of air flow though the throttle body. The butterfly valve is mounted on a throttle shaft, which is in turn coupled to the vehicle accelerator pedal, and possibly other actuating mechanisms.
The air intake system operates most accurately when there is no air leakage in the system. With minimal leakage, mass air flow sensors, which are also mounted in the air intake stream, will obtain more accurate readings of the air flowing into the engine, which, in turn, allows an on-board computer to operate the engine at peak efficiency.
One potential source of leakage is around the throttle shaft where it mounts to the throttle body housing. In order to maintain smooth rotation of the throttle shaft, bearings are typically employed that mount to the shaft and are fixed to the housing. But the need to seal around the throttle shaft still exists. Some designs do not do anything about the leakage and just allow the resultant inaccuracy to occur. Other designs employ rubber seals that mount adjacent to the bearings around the surface of the throttle shaft, but these seals can wear and create a drag on the shaft causing resistance to smooth rotation of the shaft. Although, having seals avoids the problems with leakage, especially the inconsistency of leakage from one car to another.
Still other designs employ O-rings mounted within a circumferential groove formed in the shaft at the locations of the bearings with the O-rings mounting between the shaft and bearings to seal between the two. The design maintains ease of assembly and also keeps costs to a minimum. However, the groove in the throttle shaft also weakens the shaft itself, requiring a slightly larger diameter for the same applied forces. A minimum throttle shaft diameter is desirable to save weight and cost. Therefore, a desire exists to allow for easy and cost efficient assembly of a throttle shaft to bearings in a throttle body while sealing the space between the throttle shaft and the bearings, but not weakening the throttle shafts or interfering with smooth rotation of the shaft.
A further concern that arises with throttle shafts is that they typically mount, at one end, to a throttle position sensor. Since the throttle shafts must be free to rotate relative to the throttle body housing, they typically have play in an end-to-end (axial) direction. In order to account for this play, the throttle position sensor must be more complex and expensive because it generally needs additional bushings, springs and seals to account for this. Thus a desire exists to limit the end-to-end free play, allowing for the employment of a less expensive sensor, while still allowing for free rotation and good sealing around the throttle shaft.